About pressing of tablets

Pressing stage powdered materials

Pressing process is conventionally divided into three phases:
first - seal (or preform);
second - generation compact body;
third - volume compression formed a compact body.
At the first stage - preform - external force contributes to the convergence and compaction of the material particles by filling the voids is shifted relative to each other particles. Even at low pressures becomes noticeable seal because overcome in this effort - insignificant.
Basically, the accompanying energy is used to overcome friction: the internal friction between the particles and the external friction between the machines and the matrix particles.
In the second stage the pressing pressure is increased, whereby the sealing material is made intensive due to the different types of deformation and fill voids that provide a more compact packaging material. The types of deformation may be as follows:
deformation increases the contact surface due to elasticity, which makes the particles mutually wedged;
deformation, forcing the particles change their shape due to the plastic properties and tighter together snugly;
strain is characterized by destruction of the molded material and the brittleness of the material is defined, occurs when the pressed material arising stresses exceed the yield strength of the material by size.
Such a deformation disrupts mechanically into smaller particulate material thus there is a significant increase of surface energy, so there are conditions for the occurrence of contact between the particles.
The second step - the formation of a compact body - of the bulk material is formed having sufficient mechanical strength, the porous compact body.
At the third stage - volumetric compression formed compact body - simultaneously with high pressure values, a mechanical strength slightly varies tablets provided probably particle volume contraction and the powder granules with no visible enlargement of the contact surfaces.
By substantially no sharp boundaries between the three stages of pressing, as occurring in the second stage processes, also occurring in the first and third stages, therefore, for each stage of compression may be mentioned only the predominant role of individual processes.
Research has shown that during the compression of the particles depends on the strength of the seal character of the powder particles and granules.
Tablets produced by three methods: direct compression, by using a dry granulation using wet granulation.

Direct compression
Pressing method ungranulated powders called direct compression. Guided technological scheme of production of tablets, you can see that from the production process in direct compression eliminated three or four manufacturing operations.
Such a method of compression of tablets has several advantages, including:
reduced cycle time in connection with the abolition of a number of stages and multiple operations;
minimal amount of equipment used;
reduced production area;
reduced energy and labor costs;
possibility to obtain tablets of thermoplastic, vlagolabilnyh materials and incompatible substances.
Disadvantages of the method of direct compression include:
possible delamination tablet mass;
If compaction is carried out with a small amount of active substances the dosage can be changed;
necessary to use a high pressure.
When the forced feeding of the molded material into the matrix during tabletting, certain of these disadvantages are minimized.
Despite a range of benefits, direct compression method is implemented in mass production slowly, which can be explained by the fact that a compressible material quality productive work tabletting machines must have optimal technological characteristics izodiametricheskuyu crystal shape, good flowability (at least five to six grams per second ), high compressibility (not less than 0.4-0.5 grams per milliliter) and a low adhesiveness to the molds tabletting machines.
Such features are a few non-granulated powders acetylsalicylic acid, sodium chloride, bromide, potassium iodide, as well as some other drugs which have equiaxial (izodiametricheskuyu) form approximately uniform particle size distribution and does not contain, as a rule, a large amount of fines. Best lend themselves directly compressible powders having porosities of 37% particle size of 0.5-1 mm.
For example, the round shape of sodium chloride almost defies compression, and suitable for production of tablets is an oblong shape of the particles. Drugs such as fenilsalitsitat, lactose, and others like them coarse powders with low porosity and equiaxed particle shape have the most good flowability and they may be compressed without prior granulation process. These drugs together enough good moldability and the ability to sleep from the hopper evenly, under pressure of the mass, that is, the ability of spontaneous dosing.
Nevertheless, most of the drugs are not able to fill the matrix tablet machine spontaneously, as it contains a considerable amount of more than 70% fines, as well as causing severe interparticle friction uneven surfaces of the particles. In case taco strength enhancers are added auxiliary substances belonging to the class of moving. This method produces tablets atseltilsalitsilovoy acids, vitamins, ascorbic acid, alkaloids, phenobarbital, streptotsida, phenacetin, sodium bicarbonate.
Characteristics listed here affect control used in direct compression of substances, especially their large quantities, because in this case the quality of the tablets will depend on the process parameters directly tabletting mass, its compactibility, flowability and compressibility. INSTALLATIONS experimental method that the component particles should be the smaller, less than its concentration in the tablet mass. If the particle sizes of the components greatly differ, it is impossible to obtain a homogeneous tablet mass. It is understood that consists of a system of two fine powders will form a stable, homogeneous mixture than a system with larger particles of one component. It is desirable to observe the following conditions in order to get the optimal mixture of multicomponent drugs:
matching the particle size concentration of the individual components;
close as possible between the densities of the individual components of substances;
closest to the spherical shape of the particles.
The drug substance with conventional excipients and tabletted if it is suitable for the process of direct compression. In case with conventional drug excipients not suited for direct compression is used, such auxiliary substances which have a sufficient binding effect on the particle or using suitable for direct compression LP granules with a binder.
In pharmaceutical manufacturing tabletting powders without granulation (direct compression) made the following ways:
adding improve the technological properties of materials auxiliaries;
method of force feeding the material to be tableted in a matrix of the tableting machine hopper;
provisional directional crystallization of the molded material.
Provisional method of directional solidification is one of the most complex manufacturing processes suitable for extrusion of drugs, it is to obtain crystals of a given substance tabletiruemogo humidity, compressibility and flowability method lists defining the conditions for crystallization. As a result - the preparation of crystalline drug forms with izodiametricheskoy crystals precipitating from the funnel freely and readily undergoes volumetric dosing as a result, which is a prerequisite for direct compression. This method is used for the manufacture of tablets of ascorbic acid and aspirin.
In the direct compression process for enhancing the moldability of the medicinal substances in the powder mixture are added by dry binders, most often microcrystalline cellulose (MCC) or polyethylene oxide (PEO). Microcrystalline cellulose has a positive effect on the process of releasing LP thanks to its water absorption capacity of the individual layers and hydrated tablets. When using MCC made strong, but not always easily disintegrating tablets, so together with the MCC to improve tablet disintegration recommend adding ulypraamilopektina.
Excellent communication ability in the dry state, and improved ductility gives vinylpyrrolidone Copovidone with a small particle size. The analysis presented binders showed that the production of tablets by direct compression, one of the best bonding effects has Kollidon VA 64 fine.
As binders in direct compression are recommended for modified starches, chemically react with the LP and significantly affect their biological activity and release. As means for improving the flowability of the powders used are often milk sugar and granulated calcium sulfate, which has good flowability and provides a production of tablets with a good mechanical strength, which also contributes to the cyclodextrin, which increases the mechanical strength and disintegration of tablets.
Maltose ensures uniform filling rate and has little hygroscopic and is recommended for direct compression. Furthermore, also, mixtures of crosslinked polyvinylpyrrolidone and lactose. Good flowability is anhydrous lactose, capable of directly compressible, and does not lose its properties even in the case of tableted grinding it to a fine powder, in spite of the fact that its fluidity with reduced. Spray-dried lactose microcrystals comprised of - particles and glassy amorphous structure. Lactose has good moldability due to the combination with spherical shape and microcrystals.
In some cases the mixture becomes suitable for compression by the addition of small amounts of substances such as airgel (calcium silicate), and aerosil. For example, to improve the flowability of the mixture, the optimum additive amount of Aerosil is from 0.05% to 1%.
The production of tablets by direct compression technology is thoroughly stirred with the desired drug dose and the excipients followed by compression on a tabletting machine. We can say that now, in the preparation of drugs for tableting granulation continues to be a major technological operation. However, due to the obvious economic benefits, direct compression is implemented in pharmaceutical manufacturing increasingly, which also contributes to the emergence of modern high-speed of high compression force, tablet presses.
In some cases made using tabletting process containing the necessary medicines and excipients pellets.
Pressing of tablets (tableting) on tablet machine made using a press tool incorporating two punch and a matrix representing a steel disc with a cylindrical hole in the middle diameter of 3-25 mm, and the diameter of the hole cross-section is equal to the tablets.
Matrices are fixed into the corresponding holes of the working surface - countertops. To increase the performance of the matrices, they can be made with two or three slots. The upper and lower punches are cylindrical rods (pistons) of chromium steel entering into die holes at the top and bottom and ensure the pressing of the tablets under pressure. Punches pressing surfaces are flat or concave (different curvature and radius), smooth or with transverse incisions (grooves), or even with an engraved inscription. Punches are the teams and whole, with solid punches are a single pusher unit.
Two existing type tabletting machines:
1) to the stationary funnel and the movable die;
2) with the movable and stationary funnel matrix.
The first type is called a rotary tabletting machines, revolving or revolving (the nature of the motion of the matrix system with punches). Machine of the second type are called crank or eccentric (like driving the punches mechanism) or percussion (by the nature of the pressing force). Eccentric tableting machine having a simple structure appeared earlier.

To all the questions related with production of tablets you can find answers on resource www.Tabletpress.ru